Lawinenlagebericht

Banner Summit

Sawtooth Avalanche Center
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Lawinengefahr

Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Veraltet — dieser Lagebericht ist 5 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Triggering an avalanche remains possible. Slides are more likely in upper elevation, wind-affected terrain, but could occur on wind-sheltered slopes. Triggering a large, destructive avalanche breaking deeper in the snowpack is unlikely but cannot be ruled out entirely.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Last week's storm dropped 30-40" (!!) of new snow in this zone, accompanied by strong winds. Clearing skies yesterday revealed numerous natural avalanches in the adjacent Sawtooths & Western Smokys zone, the majority of which ran on wind-loaded slopes. 

    Even though the storm has ended, wind-loaded terrain presents two lingering problems. The first is that while wind slabs (like in photo above/right) are becoming less sensitive, there are likely a few out there that you could still trigger. The second problem is that wind-affected slopes have more recent loading and a stiffer slab sitting atop buried weak layers (see Additional Discussion below).

    If someone were to trigger a slide today, it would most likely occur in wind-loaded terrain. For that reason, the best approach will be to avoid steep slopes where you find evidence of wind loading such as drifted, pillowed areas,  or feel denser/stiffer snow beneath your board(s) or sled.

    ADDITIONAL DISCUSSIONThere are a few other potential problems to keep on your radar in this Banner Summit zone:

    • In other zones, yesterday's pattern of natural avalanche activity points to a probable crust/facet layer on steep (>35 degrees) slopes that face SE-S-SW. Until we have better information on this weak layer, most of us will be avoiding steep, southerly-facing slopes—especially those affected by the wind.
    • An observer in the Banner zone yesterday found weak snow beneath the recent storm accumulations at lower elevations, possibly formed by temperature inversions last weekend. 
    • Weak October snow is buried 5-6+' deep on most shady middle and upper elevation slopes—deep enough to be very difficult to impact with our weight. Where might it still be possible to trigger a deep slab? I would still be leery of very steep (>35 degrees), rocky, wind-affected slopes at upper elevations.

    (1/8/2022) This wind slab avalanche in the southern Sawtooths released near the end of the storm. 9400', SE.

Avalanche Discussion

A BRAVE NEW WORLDLast week's multi-day storm cycle dropped 12-50" of new snow across our area, with the Western Smokys, Smoky Crest, Sawtooths, and Banner hit the hardest. Although this storm didn't change the game as much in the Wood River Valley where less snow fell, many other portions of the forecast area are dramatically different. It's time to take stock and make sense of this new world. Yesterday's clearing skies gave us a first glimpse at the pattern of avalanche activity, but we look forward to more "boots on the ground" observations in the coming days. Let's consider what we do and don't know.

Observations so far (knowns):

  • Numerous storm/wind-related avalanches occurred—not surprisingly given the massive snowfall, intense precip rates, and strong winds. 
  • Enough avalanches occurred on southerly aspects (Galena Peak, Boulders, Pole Creek, Western Smokys) to conclude a pattern exists. These slides likely failed on a crust/facet layer that was the old snow surface prior to the storm.
  • Few observed avalanches broke on the deeper October snow—at least from what we've seen so far. But here's a photo of one that did near Titus Ridge.

Observations needed (unknowns):

  • Is the crust/facet layer on steep, sunny slopes still sensitive or has it "done its thing"?
  • Will additional observations of avalanche activity show more slides that broke in October snow or reveal new patterns?
  • How deeply is the October snow buried? Where is it still a concern?

Until we get a better handle on our brave new world and the "knowns" list is longer than the "unknowns", most of us will be sticking to conservative terrain and embracing a wait-and-see attitude.

Be sure to catch up on last week's conditions in Chris' latest Weekend Update.

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